Crater lamp



mac. 28, 1948 G. H. BOUCHARD CRATER LAMP Filed Jan. 2, 1947 u. fl. r

BY; V3

ATTOQNEX Patented Dec. 28, 1948 CRATER LAMP George H. Bouchard, Ipswich, Mass., assignor to Sylvania Electric Products Inc., Salem, IMass., a corporation of'Massachusetts Application January 2, 1947, Serial No. 719,852

This invention relates to electric discharge lamps of the crater type, in which the light comes from the interior of a hollow cathode usually known as a crater. Such lamps are used for many purposes, but particularly as recorder lamps in photo-transmission apparatus.

An object of my invention is to provide a better light pattern from such craters by increasing the amount of light from the crater part of the cathode. 'VI achieve this by a reentrant portion at the closed bottom of the hollow in the cathode. The hollow may,fo r example, be in the form of a cylinder with' a reentrant cone, hemisphere, o1' the like projecting from its bottom.

Further objects, advantages and features of the invention will be apparent from the following specification.

The figure shows an electrode assembly having a cathode in accordance with the invention.

The cathode I may be of Vmisch metal, which is a well-known cerlum-containg lmetal, or of thorium or some other metal of high electronemisslvlty. I. prefer misch metal, which seems to give better life. The cathode I may be a cylinder 2 into which a hole 3, for example a cylindrical hole, extends from one end 4. A projection I4 such as a reentrant cone, hermisphere or the like extends upward from the closed bottom 5 of the hole 3. A cup B of insulating material, for example the type known as lava, may surround the hollow cylinder 2 except at its open end 4. and may extend somewhat ahead of the cylinder 2 to space the metal anode cup 1 from the cathode. The anode 1 has the opening 8 through which light from the cathode I may pass. The edges 9 of lava cup 6 may be partially bevelled, and a metal annular wire ring I0 may rest on the edges 9 to space the anode 1 somewhat further from the cathode I.

A lead-in and support wire I I extends through the bottom of insulating cup 6 and may be threaded into the bottom I2 of cathode I. An additional lead-ln wire I3 may be welded crosswise to the wire II to help hold the insulating cup 6 in place. The whole unit may then be placed in an atmosphere of gas in a sealed envelope in the manner usual in the art. A ses filling of about 18 mm. measured while the device ls still not on the usual exhaust machine,

2 claims. (cl. 17e- 122) will be satisfactory, the gas being about 94% neon and 6% argon. The anode cup may have the lead-in and support wires I5 welded to it.

When suiilcient voltage is placed between anode 1 and cathode I a thin glowing layer of gas is present on the interior cathode surfaces. 'The brightness of this glow appears to increase with the nlength of glow viewed, up to a saturation value, and the projection I4 in the bottom 5 of the hole 3 probably increases the thickness of this glowing layer in the viewing direction, parallel to the axis of the cylinder 2.

For convenience in the appended claims, the closed end of the hole or cavity in the electronemitting piece is referred to as the bottom of the hole, although it may, of course, be the top if the tube is turned around. Similarly the direction from said bottom of the hole to the open end is referred to as upward.

The gas pressure at room temperature may be in the neighborhood of 14mm. A pressure a few millimeters greater than the pressure of maximum light intensity is generally preferable to give'increased life.

The surface oli the projection I4 is preferably stepped or corrugated for greater brillancy, as

shown, but may be a smooth surface if desired.

II claim:

l. A luminous crater electrode comprising a hollow, electron-emitting metal cylinder` closed at one end only, and a conical projection extending upward inside the hollow cylinder from said closed end.

2. The combination of claim 1, and an insulating cup in which said electrode is seated.

GEORGE H. BOUCHARD.

REFERENCES CITED The following references are of record in the 

